Van Groenigen et al. (2014) introduce their publication on this extremely important topic by stating that "our global food production system faces the unprecedented challenge of having to feed a rapidly increasing world population while simultaneously reducing its environmental footprint," citing the study of Godfray et al. (2010). And since they note that "earthworms are generally thought to be essential to sustainable agroecosystems," they say "it is their supposed ability to stimulate crop growth that might be of foremost relevance to agriculture."

In light of this logical presumption, the six researchers went on to conduct a meta-analysis "to summarize the effect of earthworms on plant production across the globe," collecting some 462 data points from 58 different studies that were published between 1910 and 2013, which focused on the globe's three main staple crops (maize, rice and wheat), as well as pastures and many other food crops that were grown on all continents except Antarctica. And what did they thereby learn?

First of all, the Dutch, Brazilian and U.S. scientists report that, on average, "earthworm presence in agroecosystems leads to a 25% increase in crop yield and a 23% increase in aboveground biomass." In addition, they discovered that "earthworms stimulate plant growth predominantly through releasing nitrogen locked away in residue and soil organic matter." And they say that "in higher pH soils, the earthworm effect is significantly smaller than in lower pH soils."

Therefore, just as rising atmospheric CO2 concentrations tend to lower the pH of the water found in Earth's rivers, lakes and oceans - via what is often referred to as "ocean acidification" in the latter instance - so too would this phenomenon tend to lower the pH of the moisture found in Earth's soils, thereby optimizing the ability of earthworms to release the crop-enhancing nitrogen that is to be found in soil residue and organic matter the world over, which should subsequently lead to significant increases in crop yields the world over.